This Shared Instrument Grant application is for funding for the purchase of a Becton Dickinson FACSCalibur bench-top flow cytometer. The instrument will be integrated into the Englert Cell Analysis Laboratory, which is a Shared Resource of the Norris Cotton Cancer Center and which has been providing Dartmouth College and Medical School with flow cytometry instrumentation since 1981. The new instrument will join a FACScan bench-top flow cytometer, a FACStar Plus cell sorter, and three imaging systems in a suite of rooms in the Borwell Research Building at the Dartmouth-Hitchcock Medical Center. The need for an additional bench-top flow cytometer is base don two urgent requirements: First, the existing FACScan cytometer is heavily booked and his no longer able to provide the time and flexibility necessary for efficient research. Second, there is an expressed need that cannot be met on the existing instrumentation for four-color analysis and for the ability to use far-red excitable flurochromes. Because it has recognized the urgent requirement for the purchase of an additional flow cytometer, the Research Committee of Dartmouth Medical School has confirmed a contribution of $10,000 toward the purchase of this instrument. The Englert Cell Analysis Laboratory operates under the control of a Director, a Co-Director, and an Advisory Board, and with the technical support of a flow and an imaging supervisor. A "major user group" has been identified, consisting of eleven NIH-funded Principal Investigators dependent on the use of the flow cytometers in the Englert Laboratory for their research. This group of investigators has been responsible for 92% of the use of the FACScan cytometer in 1997 and predicts increased requirements for a bench-top cytometer in the future. They currently hold 24 NIH-funded research grants totalling $5,109,299 in annual direct costs.